[RoadTripper]

If I have an active (powered) bookshelf system (Dynaudio BM5 MKIII) and want to add a subwoofer just for kicks, is there a way to  limit the Dynaudio woofer's  low-frequency floor to some level? Or is it the case that when adding a subwoofer the primary system is electrically oblivious to the addition of the subwoofer component onto the circuit?

[JLM]

I have those same speakers.  They have 60 Hz and 80 Hz high pass filters (in addition to "flat" setting).  These "cut offs" are specifically intended to be used with subwoofer(s) to allow higher undistorted sound pressure levels.

I don't have a sub, but someday plan on it and intend to use the high pass filters.

[RoadTripper]

Thanks. I knew I could count on you. I suppose it's typical that there would be a similarly rigged switch/dial on the sub that would go hand-in-glove with the BM5 MKIIIs switch.

[JLM]

Yes, but it depends on how you connect the sub and the mains.  If you wire from amp to sub to main speakers in series you could use the sub's filter to limit what goes to the mains.  But if you wire in parallel (amp to both sub and mains) the sub's filter would not affect the mains.  In that case you'd probably end up using the filters on both sub and mains.